The present invention relates to an apparatus for extracorporeal blood treatment.
Specifically, though not exclusively, the invention can be usefully applied in an apparatus for treating kidney failure (hemodialysis and/or hemo(dia)filtration).
In particular the invention relates to an extracorporeal blood treatment apparatus as defined in the preamble of claim 1.
Such an apparatus is already disclosed in U.S. Pat. No. 4,348,280, which describes a dialysis machine provided with means for continuous preparation of dialyzing liquid by mixing water with dialysis concentrate. The dialysis machine includes a device for removing and minimizing gas in the dialysis liquid, as well as means for controlling pressure and flow rate of the dialysing liquid in the dialyzer. The means for controlling comprise a first flow rate limiter which is located upstream of the dialyzer and a second flow limiter located downstream of the dialyzer. The degassing device comprises a degassing reservoir which is continuously under a negative pressure supplied by two pumps: the first pump removing gas from the tank and the second removing degassed water from the tank. The pressure in the degassing reservoir is therefore unrelated to the dialysing liquid rate. The first gas pump is a constant speed pump producing a negative pressure in the degassing reservoir which is not affected by the flow rate of liquid to be degassed. The first gas pump is arranged on the drainage line connecting the dialyzer outlet to the discharge. The first pump is therefore useful both for applying a negative pressure on the degassing reservoir and for aspirating the used dialysis liquid from the dialyzer. The above mentioned prior art machine has the drawback of being unable to permit either a precise control over the gas quantity which has been removed from the dialysis liquid, or a regulation of the percentage of gas contained in the dialysis liquid operating inside the dialyzer. A further drawback is that it cannot estimate variation in the fluid flow rate through the vent line of the degassing reservoir.